Voi_D_ragon
Explorer
But to me, that would simply be the definition of "adventurer".I think you're reading the murder part too literally.
The phrase seems meant to be an exaggeration of what typical PCs do - wander from dungeon to dungeon, killing and looting.
Let's put it this way: a modern day adrenaline junkie goes risking his life in some way -skydiving or whatever- a D&D adrenaline junkie goes out and risks his life in some other way -namely searching for monster infested ruins and killing everyone in sight -nothing illegal or morally questionable, since monsters plague civilization and are basically bloodthirsty animals- he then proceeds to see if he can find a way to go on an even better run the next time by taking anything of value to get better equipment, thus going for bigger/more monsters, thus increasing his kick.
Similarly, anyone afflicted ("afflicted") by wanderlust today hops on a plane/bus/car and sees a few nice places before going back home. In a D&D setting, if you have wanderlust, you're walking. Through miles and miles of wild lands infested with deadly dangers, be they monsters in the true sense or barbaric humanoids that will attack you on sight. So you have to be ready and willing to defend yourself and kill these creatures. Then, it's just common sense that you pick up any shinies they have, since they might enhance your chance to survive subsequent encounters.
Point is, these people live on the edge, and you can't live on the edge by behaving as you would in a civilized context. Then they go back to civilization, sell their loot, get better equipment, and go back out on the fringe because that's their life now.
A murderhobo kills you, takes your money, and goes to a place he can spend his money without getting caught, then rinses and repeats. He could easily find a job as a mercenary, private security guard, something, but instead sees he is stringer than most and decides that might makes right, resorting to violence to attain short term gains larger than he could have if he had "followed the rules" (Why work as a guard for the merchant for 50 gp when I can kill him and become filthy rich by using his key to open his safe?)
That's my reasoning
TL;DR: murderhobos work in civilized contexts, what they do is viewed as wrong. Adventurers are seen as strange, but people understand where they travel, they have to be tough and badass.
-Again, murder- words are important